1. Field of the Invention
This invention relates to ball valves, and more particularly to ball valves having means for equalizing fluid pressure between the flow line and the valve body chamber.
2. Description of the Prior Art
Heretofore, when floating ball valves have been utilized in flow lines having relatively high flow line pressures, it has sometimes been difficult to rotate the ball valve member to a closed position. Annular pressure actuated seats are normally provided on opposite sides of the rotatable ball valve member and a differential fluid pressure area results in the annular seats being forced toward the ball valve member to grip or squeeze the ball valve member tightly therebetween. Because a fluid tight seal is normally provided between the surface of the ball valve member and the annular seats, there is no leakage of fluid from the flow line to the valve chamber in the open and closed positions of the ball valve member.
The higher the flow line pressure, the tighter the annular seals are forced into contact with the ball valve member. Thus, particularly when manually operated under high fluid pressures, such as 4,000 or 5,000 psi, manual rotation of the ball valve member from open position to closed position is very difficult, and practically impossible if relatively large differential fluid pressure areas are provided at very high fluid pressures.
If the flow line and ball valve are used for drilling mud in a drilling operation, such as a kelly or downhole valve, very high backflow pressures can result from a blowout or the like. For safety reasons, it is desirable that a ball valve can be easily rotated manually to a closed position under the application of very high fluid pressure.
When used as a kelly valve, a ball valve in the closed position may have extremely high pressure applied to the bottom side of the ball. Prior art ball valves have been extremely difficult to open for pressure control procedures due to the bottom side pressure acting to pinch the valve seats against the ball.